Water & Air by Janelle Reston

Miranda is an ordinary young woman resentful of the magic that runs in her family but has skipped her generation. If she had such powers, she certainly wouldn't be like the witches who descend on her lake resort town every summer, wasting their powers on stupid party tricks.
But when Miranda meets a water witch named Hazel, she starts to wonder if the practitioners of magic aren't so bad after all. And if reconciling herself to the world of witchcraft means she has a better chance of sleeping with Hazel, well, so much the better.
This story has mature themes and scenes of intimacy. It is intended for adults.